Multi-ply bags with stepped corner flaps



Oct. 22, 195.7V

. A. GELBKE 2,810,509 I MULTIPLY BAGS WITH STEPPED CORNER FLAPS Arron/frs.

Oct. 22, 1957 A. GELBCKE MULTI-FLY BAGS WITH STEPPED CORNER FLAPS 4 Sheets-Sheet 2 Filed Nov. 25, 1 953 N\ Q iwi Q nl rm 1 II HMMN Oct. 22, Y1957 A. GELBCKE MULTI-FLY BAGS WITH STEPPED CORNER FLAPS Filed Nov. 25 1953 4 Sheets-Sheet 5 c Q10. w 2

HIIIHIIHIHIH'I IZ-c .15: 2` j i fill- LL 5 2 l 1 -1 f 3 III|||IIIIIIIIIIIIIIIIIIIIIIIIIIII INVENTOR. EXA No5/e GEL ECKE.

ATTURNEYS.

Oct. 22, 1957 A. GELBCKE 2,810,509

MULTI-FLY BAGS WITH STEPPED CORNER FLAPS Filed Nov. 25, 1953 4 Sheets-Sheet 4 6o u I;

1 INVENTOR." L EXANDE/'i GELsc/(E.

United States Patent MULTI-PLY BAGS WITH STEPPED CORNER FLAPS Alexander Gelbeke, Rhode-St. Genese, Belgium, assigner, by mesne assignments, to St. Regis Paper Company, New York, N. Y., a corporation of New York Application November 25, 1953, Serial No. 394,438

Claims priority, application Netherlands April 28, 1951 Z Claims. (Cl. 229-55) This invention relates to multiwall bags of paper or other flexible sheet material, and more particularly to bags of that type formed with novel arrangements of stepped end closure flaps, and methods for making same.

Multiwall bags with end closure llaps of various types, with sorne or all of the flaps of stepped form have been well known for some time. In some of these it has been proposed to provide the end edges of the so-called side laps only in various stepped relations, and in others only the edges of the corner flaps. However, these known constructions have all involved certain disadvantages and difiiculties, particularly as to the stepping of the corner aps, which is important in securing a multiwall bag of adequate strength and which Vat the same time will have corner areas free of excessive stillness and brittleness caused by superposing a multiplicity of glued folded-over areas.

With the present invention, a form of stepped corner flap construction is provided with which all four corners of the bag may be conveniently made of equal strength and having the very same degree of llexibility and freedom from stiffness and yet being made with such a stepped form as to avoid cutting out and wasting any loose pieces of paper. This is accomplished by scoring or perforating a plurality of the webs of the sheet material at regular intervals transversely of their length at lines which are to deiine the end edges of the corner iiaps of the nished bags, then such webs are assembled by superposing same in such relation longitudinally that said lines on the web which is to form the outer ply of the bags, are located in positions intermediate the score lines on one under ply and those on another under ply. Then when the assembled webs are formed into a tube and the tube is separated at bag length intervals, each bag blank will have a corner flap portion, the outer ply of which may be referred to as being of normal length as compared with an under ply thereof of abbreviated length, and another of more extended length. Thus each corner of one bag will not only contribute from one of the plies forming same, material for forming an extension of one of the plies at a corner of the next adjacent bag formed from the same webs, but the corners of the next adjacent bag reciprocally contribute from one of their plies material to provide extensions of one of the plies at the corners of the first bag. Each corner ap will thus have plies of three diiferent lengths, and the ends of two of such plies at least will be in such stepped relation that the side flaps may be secured thereto respectively by stepped lines of pasting. These novel stepped corners may be formed on bags having either stepped or non-stepped side aps, or may be combined in a new relationship with stepped side flaps to provide bags, the end flaps of which are stepped all around in a coordinated way and having strength and flexibility characteristics not previously attainable.

The nature and advantages of the invention may best be understood by iirst considering the shortcomings of various of the prior stepped end bags, starting with that of German patent to Hoppe No. 557,061. While this disp y2,810,509 Patented Oct. 22, 1957 closes end closure llaps which are all stepped, with half of the circumference stepped in one direction and the other half in the other direction, yet at one corner the steps face the inside of the bag so that the outer ply only of such corner can be pasted to the side liaps when the latter are folded over. If the side liaps are to be pasted to more than one ply of a corner flap, as is highly desirable for strength, such corner flap must, of course, have stepping which is open, that is, stepping which faces outwardly of the bag to permit a plurality of ply ends to contact with and be pasted to the side llaps. Also the construction of this German patent has the disadvantage that portions of the steps on the corners which do have open steps are too short for being properly overlapped by and properly pasted to the side aps, and furthermore, the end portions of the side flap steps cannot readily and properly be covered when the flaps are all folded down.

In the bag of U. S. patent to Robinson No. 2,073,222, while all end closure flaps are stepped, the necessary reversal of the direction of stepping on one side as compared with the other occurs midway of each corner flap. This involves making certain angular wasted cut-outs and also incurs very complicated folding operations. Furthermore, if one of the corners is to be used as a valve corner, since the steps will have angularly shaped gaps and be half open and half covered, the corner requires application of a special valve reinforcing area of paper.

Further proposals to provide stepped corner aps are disclosed in Hoppe et al. U. S. Patent No. 2,176,499, but here the stepping is accomplished only by complicated constructions which also involve the forming of wasted cut-out pieces.

Another proposal is shown by U. S. patent to Hoppe No. 2,122,061, whereby all plies of the valve corner flap are extended in length by utilizing material cut from a corner of the next succeeding bag tube being formed, but this results in a relatively stiff corner fiap yattained by substantially weakening another corner with no compensating advantage.

Coty U. S. Patent No. 2,346,292 shows another variation wherein the outer ply of two corner flaps is extended by utilizing material cut from two corners of the next succeeding bag being formed, but this and Iall similar prior expedien-ts, so far as I am aware, have been such as to destroy the uniformity or harmony of the bag construction in respect to the matter of providing stepped corners all of which will be equally free of weakness or excess stiffness and not involve wasted cut-outs.

in View of the difliculties above pointed out with the prior stepped corner constructions, the multiwall bag industry in this country and most others, has found it preferable to forego the provision of stepped corner flaps in stepped bags. Yet the forming of bags with properly stepped side aps, but with unstepped corner aps results in a considerable abbreviation of the corner llaps as cornpared with the length which they should desirably have. in order in some measure to counterbalance this abbreviation and increase the overlapping of the corner and side flaps, cuts have been made between them but withsuch cuts the construction still is such that there is danger that the corner aps will be .blown out, during or after the filling of the bag, especially at the valve flap, because the unstepped valve flap is still not as long as advisable. This fact, among others, has led to the common practice of going to the trouble and expense of pasting a reinforcing slip or an extension of some form onto the valve llap. Furthermore, inevitably interpasting of the plies of unstepped corner iaps involves the use of superposed lines of glue, so that the corners become brittle, relatively inflexible and liable to breakage due t-o stiffness, especially when the number of plies is increased.

While the above discussion principally concerns valve bags of the type having pasted stepped corner and side aps at both ends, the invention also contemplates following similar principles in making open mouth bags with the bottoms only formed with pasted stepped side and corner flaps. That is,` in forming open-mouth bags according to the invention, the procedure may be the same as for making pasted end valve bags, except that in separating the previously prepared multi-plyv tube into bag lengths, at alternate intervals the tube is cut straight across (along a line coinciding with what are to be the open mouth edges of two bags); whereas at intervening intervals, one bag length is separated from the next along lines which have been previously perforated to demark the above-described special stepping of the bottom corner aps of two bags.

The invention in another of its phases is also adapted for use in making sewn end valve bags in which there is but one corner flap viz. a corner flap `specially stepped in accordancewith the invention. ln this case, in preparing the multiply tube for severing into bag lengths, perforations are made in the webs only at the regions where stepped valve ilap edges are to occur. That is, in separating the multi-ply tube into bag lengths, the tube is cut straight across at lines which are to form the bottom edges of the bags and also cut straight across at lines which are to form the top edges of the bags except for the region of the valve flap. At the valve flap region, the transverse perforations are so made that the inner edges of the outer ply of the valve flaps are of intermediate or normal length, whereas at least one under piy is of more extended length and at least one other under ply is of a correspondingly abbreviated length. The paper constituting the extended length is taken from the area where the abbreviated length is to occur on the next adjacent bag. And the extended length in such next adjacent bag is formed of paper taken from the abbreviated ply of the first bag. This procedure makes possible a valve flap on each bag in which the plies are at least of three dierent lengths, one being long enough to perform the functions of an inwardly directed valve sleeve such as has heretofore generally been formed by using a supplemental sheet. Such flexible valve iiap extensions have also been proposed to be made integral with one of the intermediate plies by taking the required paper therefor from the side wall cf next adjacent bag near the bottom thereof, as disclosed in U. Si. Reissue Patent No. 23,230, granted to Harry E. Lee, but the method of that patent may, under certain circumstances, tend to cause weakening of the side wail areas of the bag adjacent the bottom, since at such areas paper has to be cut out from the intermediate ply which then becomes too short at such areas to be caught in the bottom closure seam. With the present invention, ..is shortcoming is avoided, since the necessary paper for the extended ply is taken from the abbreviated valve ap ply of the next adjacent bag and this involves no detriment, but rather an improvement of the valve tlap since its inner areas will have at least three steps and will therefore be less abrupt and more flexible for insuring secure closing of the valve.

Various further and more specific objects, features and advantages of the invention hereof will appear from the detailed description given below, talzen in connection with the accompanying drawings which form a part of this specification, and illustrate by way of example the presently preferred embodiments of the invention.

In the drawings:

Fig. l shows an assembly of three superposed webs with transverse weakened or cut lines thereon respectively in proper relative positions for defining the end edges of .the corner flaps of the finished bags made according one example of the invention;

Fig. 2 is a view of the same webs as of Fig. l after same have been folded and formed into a tube, this figure also indicating the positions of certain ap fold lines and slits for separating the corner liaps from the side flaps, according to one embodiment of the invention;

Fig. 3 is a view of one of the separated bag lengths formed from the tube as of Fig. 2 and also indicating by daslndot line A-B how this bag length may be cut into two bag blanks for forming two open mouthed bags, as hereinafter explained; that portion of Fig. 3 above the dot-dash line C-,D may also be treated as being constituted of a tube separate from that portion below the line C-JJ' and in which event, if these tubes are separated along line A-B, there will be provided four separate bag tube blanks, each having a stepped valve flap for making sewn end valve bags as per Fig. 6 hereinafter referred to.

Fig. 4 shows a bag made from a bag length as shown in Fig. the left hand end of Fig. 4 showing the appearance of the bag after the corner flaps and side flaps have been folded to closed position to form a ilat bottom for the bag, and the right hand side of Fig. 4 showing the corner flaps folded in, but with theside iiaps still open;

Fig. 5 is a view similar to Fig. 4 except that in Fig. 4 the side and corner flaps are separated by slits, whereas in Fig. 5 the side and corner iiaps are joined by diagonal folds;

Fig. 6 shows a valve bag with sewn end closures, and with a stepped valve flap made according to one phase of the invention;

Fig. 7 is a view similar to Fig. 5', but showing the application of the invention to a bag having stepped side flaps separated by slits from the corner flaps;

Fig. 8 is a view showing a bag end closure made with a novel form of stepped side flap construction correlated with corner flaps similar to those of Fig. 5, the left hand end of Fig. 8 showing the aps all in closed position, and the right hand end also showing the aps all in closed position, except that the outermost side flap is shown before being folded to closed position;

Figs. 9-il, inclusive, show the manner in which the end portions of three plies may preferably be cut for a bag end as of Fig. 13 and similar to the bag end of Fig. S;

Fig. l2 shows the manner in which the three plies of Figs. 9-11 are preferably assembled;

Fig. 13 shows the end of a bag made from the assembly of Fig. l2 and with the corner tlaps folded in, but with the two side flaps still open;

Fig. 14 illustrates a modification of the construction of Fig. 13, and

Fig. l5 is a view of another embodiment of the invention similar to that of Fig. 7 but showing a construction in which the slits between certain of the side liap plies and corner flap plies, respectively, are in stepped positions, so that a construction is provided which will have unusually elective sift-proof characteristics.

Referring now to Fig. l in further detail, three webs of paper or other tiexible sheet material from which the bags are to be made are here shown in superposcd assembled relation, the webs being identilicd respectively by the numerals 1, Z and 3 applied to the edges of the webs, the same numerals in this ligure as well as in other figures being sometimes applied to lines of perforation or cutting to identify the web in which the cut or line is formed. While in this ligure (as well as in various other figures) for simplicity only three webs are shown for forming a threeply bag, it will be understood that, if desired, for bags with a greater number of plies, any one or all of the webs may be duplicated, that is, two or even more webs of identical outline and configuration may be used. Also, either all of the webs may be of paper, or some or all of same may be of other tiexible sheet material suitable for forming multi-wall bags.

Preferably before the webs are superposed as in Fig. 1, each of same is perforated respectively along lines as at a-b, c-d and e-f, these lines serving to denne the inner end edges of the corner flaps of the finished bags. Such perforating may be accomplished for example by using perforator equipment suitably adjusted, such as shown in U. S. patent to Lienart 2,581,801, granted January 8, 1952, the webs, after being perforated individually, being assembled by superposing them in such relation longitudinally that the lines of perforation will be in the positions shown. That is, the lines c-a' cn the web which is to form the outer ply of the bags, are located at positions intermediate and preferably half way between the lines 'awb on one under ply, and the lines e-f on another under ply. The term under ply as used herein is intended to refer to either or any of the plies other than the ply which is to form the outside of the finished bags.

lt may be here noted that the lines 1 -b, c-d, and e-f, while preferably comprising lines weakened by perforating, could, if desired, depending on the type of tuber equipment used, be in the form of transverse cuts instead of perforations, and for convenience such lines, however made, will be hereinafter referred to as score lines.

The position of the score lines a-b will hereinafter sometimes be referred to as being in advance of the positions of the score lines c-d, and the score lines e-f will sometimes be referred to as spaced rearwardly from the lines c-d.

The webs 1, 2 and 3 as shown in Fig. 1 are preferably assembled with their longitudinal edges relatively stepped as shown, and as the assembly passes through the usual tuber machine, it becomes folded along the two horizontal dot-dash lines shown in Fig. l, to form a flattened tube, as of Fig. 2, the longitudinal stepped seam of which is pasted in the usual way.

As will be apparent from Fig. 2, after the continuous multi-ply tube is formed, the score lines above referred to will be locatedat the proper positions at the foldedover edges of the tube to dene the end edges of the corner flaps of each bag length, after the tube is separated into sections as shown in Fig. 3. The dot-dash lines 20 in Fig. 2 indicate the location of the future fold lines which will occur along the median lines of the top and bottom end closures of the bag during the formation of the closure flaps. The dot-dash lines as at 21 in Fig. 2 indicate the position of the diagonal fold lines which will define the outer limits of the corner aps when folded in to form the bag end closures.

If the corner and side flaps are to be separated by slits as for the construction as of Fig. 4, for example, then the ends of the score lines, as shown in Fig. 2, are interconnected by longitudinally extending cuts or slits 22 which extend through all plies of both the front and back surfaces of the bag. These cuts may be formed on the tuber machine in well known ways, either before the tube is formed as of Fig. 2, or thereafter, and before the continuous tube is separated into bag lengths. It is evident that the separation of the corner flaps from the side flaps by cuts can be also limited to some of the plies. To form aps as per those on the bag of Fig. 5 for example, the cuts such as at 22 would be made in the under plies but not in the outer ply.

After the continuous tube is formed, as of Fig. 2, to produce bag blanks as of the form shown in Fig. 3, the tube is transversely cut into sections along lines as at 23, these cuts passing through all of the plies andthrough both the front and back surfaces of the bag, and serving to interconnect the mid-portions of two of the slits 22 which are located adjacent two opposite corners at one end of a bag.

From Fig. 3 it will be noted that all four corners of the bag blank there shown are identical, except that at the two corners on one end of the bag blank, the innermost ply 3 is extended and the intermediate ply 2 is abbreviated, whereas on the other two corners, the innermost ply 3 is abbreviated and the intermediate ply 2 is extended. Thus for practical purposes, and at least so far as concerns strength, flexibility and freedom from excess stiffness, all four corners will be equivalents. And while a small amount of material is sacrificed from one ply at each corner to provide material for an extendedl ply onthe cor-f ner of the next adjacent bag, yet that corner of the next, adjacent bag in turn reciprocally provides for an extension on the corner of the first bag. Any tendency for loss of strength due to abbreviation of one ply at each corner, is more than compensated for by the extension of another ply at the same corner, for the reason that the end edges respectively of each ply on each corner flap will b-e spaced apart in stepped relation, and hence the glue lines for adhering such edges to other plies can be spaced apart, rather than being superposed. Thereby the available paper of the several plies of the end edges of the corner flaps is distributed over wider and more exible areas, free from troublesome stiffness and brittleness, and providing corner aps al1 'of uniform over-all length, each long enough not to blow-out.

The assembly of Fig. 3 may, if desired, be cut into two along the transverse dot-dash line A-B to provide vtwo halves, each comprising a bag blank suitable for forming bags, each with a pasted stepped corner bottom, but each having an open mouth (formed at the line A--B). It will be evident that if this practice is t-o be adapted, the groups of score lines ab, c-d and e-f should be made at intervals of two bag lengths, and for that purpose in practice the assembly as shown in Fig. 3 would usually be relatively longer than here shown, if open mouth bags are to be formed of customary proportions.

In a further embodiment of the invention, the transverse perforating of the webs may be omitted on what is to constitute one edge of the flattened bag tube. That is, such perforations will be made only at intervals of two bag lengths lat one edge of the flattened tube. Or in other words, that portion of Fig. 3 above the dot-dash line C-D as above stated may be treated as constituting'a tube separate from that portion below the line C-D, and hence (such tubes severed at line A-B) this figure may be considered as representative of four separate brag tube blanks, each having a stepped end valve flap area. After such flap areas have been folded in to form the valve, these bag blanks may be closed by sewn seams with closure tapes as indicated at 25 in Fig. 6. Here it will be noted that the valve flap outer ply 1 is of intermediate or normal length, whereas at least one under ply is extended. This extension in alternate bag lengths will be on ply #3 and in the intervening bag lengths, the extension will be on ply #2. And Ianother under ply willbe abbreviated, that is, in alternate bag lengths the abbreviation will be on ply #2 and in the intervening bag lengths on ply #3. It will be noted that the portions of the extended ply will be caught and retained by the closure seam and thus `the extension will serve to provide the functions of the conventional socalled notch present in the common types of sewn end valve bags. To form such notches in the conventional way, la narrow transverse strip of the multi-ply bag tube has to be cut out and thrown away as is well understood in the art, but with the present invention vthe extended ply providing the functions of a notch, can be made without the necessity of cutting out and wasting any of the paper since the paper used in making such extension is provided by abbreviating 'another under ply'of the valve flap of the next adjacent bag blank.` A valve ap having in full the advantages as to flexibility of three steps at its inner end may thus be formed without any wastecut-outs of paper whatever, and the valve flap will have a flexible single ply extension acting as a notch and formed without going to the expense of'using any supplemental sheet or sleeve and Without sacrificing any strength where needed at the valve area. The bags as of Fig. 6 may be formed either with or without gussets such as indicatedfby the dotted lines 27 along their vertical edges.

Reverting now to Fig. 4, the two corner flaps at the right hand end of the bag are here shown folded in, in position to form the corner portions of the end closure separated by the slits 22 from the side flaps, which are here shown prior to being folded in place. The side flapsv may be folded inwardly, one overlying the other, by fold-V ing along base fold lines as at 28, after which the end closure will have the appearance shown at the left hand end of Fig. 4. A

It may be noted that any one of the four corners of Fig. 4 may be utilized as the valve corner, since all are of the same strength and degree of flexibility, and all provide flaps with an inwardly extended flexible ply, well adapted for secure valve closing purposes.

While at both corners of the left hand ends of Figs. 3 and 4, it is the intermediate ply which is abbreviated yet the score lines, if desired, could just as readily be so made that each end of the bag would have one corner with an abbreviated innermost ply and another corner with an abbreviated intermediate ply. This possibility is shown, in fact, by the diagrams of Figs. 9-13.

The above description as to Fig. 4 also applies to Fig. 5, with the sole exception that here the slits separating the main portions of the corner and side flaps are omitted, as may readily be done in many cases, while still providing a bag end closure with corner aps of adequate length. It will be readily understood that also the corner iiaps with one or several inner plies without slits, can be combined with one or several outer plies with slits.

In Figs. 3, 4 and 5, the outer ply of all of the corner flaps is of normal length; that is, before the aps are folded in, the outer ply of each corner flap is of such length -that its end edge will be on the same level as the end edges of the main body portion or remainder of the bag blank between the corners. Also, with the forms of the invention described below and which have stepped side aps, the outer ply (referred to as of normal length) at each corner (before the flaps Iare folded in) is of a length such that its end edge will be -on a level with a line which is substantially mid-way between the lines along which the longest and the shortest steps of the side flaps terminate.

In Fig. 7, the invention is shown as applied to a bag end closure which has stepped side flaps, so as to give the substantial advantages of a bag having all of its ilaps Y stepped in a logical way to permit the stepped areas on each ply of each ap to be individually pasted respectively to a stepped area on one ply of another iiap. As shown in Fig. 7, the steps 30 of the various plies on one side flap (which is to be the underlying side flap) are positioned respectively so as to come in contact with the steps 31 on the other side flap (which is to be the overlying side iap). Thus the side fiap steps have what will be hereinafter referred to as a coordinated relationship. The left hand end of Fig. 7 shows the bag end yclosure completed with the stepped side aps folded in position one to overlie the other in the proper stepped relation 'and with the end portions of the side Hap steps overlying steps on each corner flap in a manner whereby a plurality of corner flap steps may be pasted directly toa plurality of side flap steps, thus insuring a most effective strong seal.

While in Fig. 7 the corner aps are separated from the side flaps by slits, with the construction shown in Fig. 8, such slits are omitted and an arrangement of cooperating corner and side flap steps is provided, having certain distinct advantages which will be hereinafter described.

The corner flaps of Fig. 8 may be made by providing score lines the same as for the previous figures. The side aps respectively are stepped as at 32-33 in a coordinated way, the length of the side flap steps preferably being equal to the dimension marked A--B of Fig. 8. Thus when the side flaps are folded over, the diagonal folds thereof will intersect at points A and B which, it will be noted, are spaced by a distance somewhat greater than the dimension A'- This has a number of advantages of substantial importance not heretofore secured with attempts to provide multiwall bag end closures which are stepped all around." First it will be noted that the overlaying side ap when folded down (see left hand end of Fig. 8) will be such as to completely cover all of. the stepped areas 'on the underlying side ap. Next,

V`8 it will be noted that outwardly of the intersection points A-B there are vno side ap areas overlying the exposed diamond shaped endflap areas and thus the diagonal folds at points A and B form a vertex with strong folded over edges, so that if any one of the corners is to be used as a valve corner, the upper side of the valve at its outlet wiil be constituted of folded-over-junctures of the corner and side flaps and will have great strength against tearing. It will be appreciated if, as in some prior constructions, the ends of the stepped portions of the side flaps extend out beyond intersection points such as at A and B, then the upper outer portion of the valve opening would comprise in part an easily torn stepped ply of paper and in other parts stepped areas, the steps of which may catch on the filling tube when filling the bag. Since a considerable part of the weight of the bag when being filled is supported by the Valve areas, it is important that the upper or cover side of the valve be as Vstrong as possible. In order further to reinforce this area, preferably the outer step on each side flap is terminated at its ends, as shown in Fig. 8, along an angle such that the ends of the step in effect constitute continuations of the diagonal fold lines, that is, the outer ply step 32 on the underlying side ap terminates along angularly positioned lines as at 34, 34' and the 'corresponding outer step 33 on the overlying side lia'p terminates at its ends along lines 35, 35. As

a result, the outer ply of neither of the side flaps has any cut ot edges near the intersection points A and B. Furthermore, the areas indicated at 36, 36 are so positioned as to come into contact and be pasted to areas 37, 37. These latter areas form parts of the extended corner flap ply portions and the pasting of same to the outer ply of the underlying side flap in this way contributes to the strength at these areas. v

Fig. 9 shows how the end edge portions of the outer ply may be cut to form the outer ply of a bag as of either Fig. 8, or Fig. 13.

In Figs. 9-13, inclusive, the edges of each ply have distinctive cross hatching marks thereon to more clearly distinguish the edges of one ply from those of another in the assembly.

Figs. l0 and 11 illustrate how the end edges respectively of an intermediate and innermost ply may be cut for forming a bag end as of Fig. 13. Y

Fig. 12 shows the web end portions of Figs. 9-11 in proper assembled relation and ready to be folded into a tube.

In Figs. 9-14 inclusive, the extended and abbreviated plies at one corner are made complementary to the abbreviated and extended plies of the other corner of the same end of the bag. This avoids on the Idrawings any necessity of illustrating the contours of the ends of the plies for the other end of the bag, which may in all respects be complementary to the ends shown in Figs. 9-14. In practice, however, it will in most cases be preferable, as indicated in Figs. l-5 inclusive, and 7, to make both corners of one end of the bag with the same ply abbreviated and with another underply extended at both corners of :su'ch bag end.

The form shown in Fig. 14 differs from that o f Fig. 13 in that only the middle portions of the corner aps are stepped, that is, they are stepped only for a distance suflicient so that the steps extend out as at 40 at each end slightly beyond the base fold lines 28-28, and con` sequently the corner ap steps may readily be increased in width somewhat, that is, the extended ply of each corner may be readily extended somewhat more than in the case of Fig. 13. Also the corner ap Shown in the left hand side of Fig. 14 is so formed at its extended ply or step as to have a cut-out 41 and the abbreviated ply is so formed as to have a corresponding extension 42 at its mid-portion. It will be understood that the material taken from the cut-out area l1-will |serve to form an extension, such as at 42, upon the abbreviated ply of Vthe corner ap of the next bag and reciprocally the extension 42 will in effect-be cut out from the extended ply of the next bag. The cut-out 41 facilitates entrance of material into the bag when this corner is being used as a valve corner and the extension 42 at the same time serves some what to strengthen this corner when used as a valve corner.

In all of the above-described embodiments of the invention which have stepped side flaps, as will be clear from Figs. 9-12, none of the corner iiap steps corresponds in length to any of the side ap steps on corresponding plies. That is because on the corner liaps the outer ply is of normal length (as hereinabove defined), whereas on the underlying side flap the outer ply must be abbreviated and on the overlying side ap the outer ply must be extended. But if on the corner aps the outer ply should be either substantially extended or abbreviated (contrary to the principles of this invention), it would be impossible to make all of the four corner flaps of the desired uniform equivalent construction and with the corner flaps all of equal strength with equal pasting areas if obtained by separating an endless multiwall tube into sections.

With all of the forms of the invention it will be understood that the superposed areas of the various ply ends may be interpasted in customary ways. Also the portions of the underlying side iiap which overlie corner liap areas are pasted to the latter in the usual way except at the valve corner, and the portions of the overlying side flap which come into contact with the underlying side iiap are pasted thereto. The end portions of the overlying side flap are also pasted to such areas of the corner liaps as come into contact therewith, except at the valve corner. However, the interpasting of the plies in the corner aps may usually be confined merely to spot pasting the abbreviated ply portions of the corner aps to the ply or plies which have areas contacting therewith. In other words a considerable portion of the customary interpasting of the plies in the corner aps may be dispensed with, thus leaving such flaps in much more pliable nonbrittle condition than in bags where the corner flaps have no stepped elect `or where the steps have to be interrupted part way across the edge of the flap.

All of the embodiments of the invention have the advantage that the way in which the corner ilaps join the side flaps in all cases is the same at both sides of each of the four corners of the bag and thus well adapted for uniform engagement by the mechanism used in bottoming the bag. The forms of Figs. 8-14 inclusive are particularly well adapted for high speed bottoming operations.

Referring now to the embodiment of Fig. 15, as above stated, there is here shown a construction similar to that of Fig. 7, except that the slits between certain side flap plies and corner ap plies are positioned in stepped relation. That is, for example, referring to the corner indicated generally by the numeral 50, the slit line at 51 which forms the end edge of the inner ply of side ap 52, is stepped inwardly of the corner of the bag somewhat as compared with the slit line at 53 which forms the end edge of the intermediate ply of the same side flap. The outer ply is also slit along a line 53a which is in alignment with the edge 53. Thus the side edges of the outer and intermediate plies of the corner flap 50 will occur along a line 54 which is stepped inwardly as compared with line 55 along which the side of the inner corner flap ply terminates. With this construction it will be noted that when the side ilap 52 is folded over along base fold line 56 the inner ply of the side flap will come in contact with and may be pasted directly to extensive areas of both the inner ply and the outer ply of the corner flap. At the same time the end of the intermediate ply of the side iiap will come into contact with and may be pasted directly to the outer ply of the corner ap. Furthermore, the edge portion indicated at 57 of the inner ply of the corner flap may be pasted directly to the outer ply of thecorner flap and pasted partially back upon itself. Accordingly, an extensive doubly secure sealing effect may be obtained between the corner llap and the underlying side liap. It will be noted that the construction is similar at ,the areas where the overlying side ap 60 joins the corner flap 50 except for the fact that the steps on' the side flap 60 are coordinates with those on the side flap 52. The construction at the other corner 61 of the same end of the bag may be like that at the corner 50 as above described. The constructions at the two corners 62, 63 at the other end of the bag are also similar to those above described except that here it is the intermediate ply of the corner flaps rather than the innermost ply thereof which is extended more than the outer ply while the inner ply is abbreviated as compared with the outer ply.

It will be understood that instead of having both corners at one end of the bag alike as shown in Fig. 15, diagonaliy opposite corners might be made alike with the other two diagonally opposite corners also alike. But in either case, all four corners will have flap portions of equal extent, strength and degree of flexibility. And

the bag length as shown in this Fig. l5 may be cut from a continuous tube without any waste cut-out areas, thus eliminating waste of paper and the annoyance of disposing of any cut-outs. While in Fig. 15 the slits between side and corner flaps are such as to provide two steps, yet such slits with bags having three or more plies may, if desired, similarly have three or more stepped slits independent of each other for each ply.

While the construction shown in Fig. 15 provides for unusually secure sealing of the bag corners against sifting, yet the overlying side flaps will at their edges at the valve corner be comprised only of two plies at certain points and thus the valve corner may not have the strength available, with the construction of Fig. 8, yet any difficulty in this respect may be overcome by use of well known types of valve sleeves in the valve corner.

This application is a continuation-in-part of application Serial No. 282,350, filed April l5, 1952, on which Patent No. 2,729,150 was granted on January 3, 1956, and in so far as the subject matter of that application is common to the present application, applicant relies on the priority rights afforded by that application.

Although certain particular embodiments of the invention are herein disclosed for purposes of explanation, various further modifications thereof, after study of this specification, will be apparent to those skilled in the art to which the invention pertains. Reference should accordingly be had to the appended claims in determining the scope of the invention.

What is claimed and desired to be secured by Letters Patent is:

1. A multiwall bag having at least three plies formed respectively of separate sheets and having at each end a closure comprising folded-in corner aps and a pair of overlying side flaps, the side flaps joining the corner aps along diagonal fold lines, -the side flaps being at least in part separated from the corner flaps by slits, the outer ply of each corner flap beng of normal length, one under ply being of more extended length on each corner flap and as compared with at least one other under ply of more abbreviated length on each corner flap, the lengths of the under plies respectively of two of the corner ilaps being complementary to the length of the under plies respectively of the other two corner flaps, the corner flap ply portions which are abbreviated being all of substantially the same length and those which are more extended being all substantially of the same length, and all of the plies of all of the side and corner iiaps being of such length that a series of bag tube lengths to form such bags can be cut from a continuous multiwall tube by transversely severing the plies of the tube along lines which define the end edges of the bag flaps without forming Waste cut-out areas,

the total outer ply surface area on each corner Hap available for pasting to overlying flap portions being approximately the same as on all of the other corner flaps.

2. A multiwall bag in accordance with the foregoing 5 claim 1 and in which the side aps have coordinated stepped end portions, and in which the outer ply of each of the corner -aps which is of normal length, terminates approximately midway between the terminal edge of the accompanying more abbreviated ply and the 10 terminal edge of the accompanying more extended ply.

References Cited in the le of this patent UNITED STATES PATENTS Lee May 16, 1950 Robinson Mar. 9, 1937 Hoppe June 28, 1938 Hoppe Oct. 17, 1939 Tooker Feb. 18, 1941 Coty Apr. 11, 1944 Jones Feb. 2, 1954 Grasset Sept. 4, 1956 Owens Sept. 25, 1956 

